1. Field of the Invention
This invention relates to a rear projection type image display device using one or more liquid crystal panels or the like, comprising a single projection lens and a screen.
2. Description of Related Art
As a transmission type screen of a rear projection type image display device using one or more liquid crystal panels or the like, which is provided with a projector comprising a single lens, the transmission type screen constructed as shown in FIG. 10 has been used heretofore. In this type screen, there are a Fresnel lens sheet 11 having a Fresnel lens on the surface of a transparent resin plate, a lenticular lens sheet 12 having semicylindrical convex lenses repeatedly formed in the horizontal direction on both sides thereof, and a front plate 13 using for the purpose of protecting the lenticular lens sheet or the like.
In the screen shown in FIG. 10, a fine particles diffuser of quartz, glass, polymer or the like is mixed with the lenticular lens sheet 12 in order to increase the vertical angle of visibility in addition to the horizontal angle of visibility. Further, the fine particles diffuser is similarly dispersed in the Fresnel lens sheet 11 for the same purpose.
However, the conventional transmission type screen has problems in respect of distinction and contrast of an image. It is known that as one cause for degrading the distinction and contrast of an image, cited is the so-called ghost light such as stray light, which is unnecessary reflected light or the like generated from members for forming a projection optical system such as a projection light source, an enlargement lens, a Fresnel lens sheet and so on. Conventionally, in order to reduce the stray light or the unnecessary reflected light, members for forming a projection optical system have been painted black, and also the surface of the non-lens surface (e.g. the opposite surface to the lens surface of the Fresnel lens, the rise surface or the like) of the Fresnel lens has been roughened, but the effects could not been satisfied.
As another cause for degrading the distinction and contrast of an image, cited is that the outside daylight such as interior lighting or the like is reflected in the inside of a lenticular lens or on the surface thereof. As shown in FIG. 11, the outside daylight 14 incident from the observing surface side (opposite side to the projector) is diffusion-reflected by a fine particles diffuser 15, and the diffusion-reflected light 16 is returned to the observer side, so that the whole surface of a screen becomes white to degrade the contrast of an image projected from an image source.
In order to solve the problem that the distinction of an image and the contrast of an image are low, as disclosed in Japan Patent Laid-Open No. 49-12943, Japan Patent Laid-Open No. 58-59436, and Japan Patent Laid-Open No. 58-134627, black stripes 17 as a light shielding member has been provided on the surface of the observing surface side of the lenticular lens sheet 12 (See FIG. 11).
In this case, if the black stripe ratio (the ratio of the black stripe width to the lenticular lens pitch) is high, it is apparent that the degree of degradation of contrast due to outside daylight becomes lower. But in a three-CRTs image display device, angles of incidence on the lenticular lens sheet from three tubes are different, so a color shift correction is required because light from the respective projection tube is converged on each of different positions of an outgoing lens of the lenticular lens sheet. Accordingly, the black stripe ratio is generally 50% or less.